The present invention relates generally to a process for the extraction, production and purification of carbon dioxide gas. More particularly, it relates to the use of a biological molecule, namely carbonic anhydrase, to effect the reversible hydration of carbon dioxide. Carbonic anhydrase can be used for the production, purification of carbon dioxide and the products of the hydration reaction, hydrogen and bicarbonate ions. Specifically, the invention relates to a process whereby immobilized carbonic anhydrase contained within a reactor device catalyses the reversible hydration of carbon dioxide. The invention also relates to an apparatus for performing the process. The process may be employed for the production of hydrogen and bicarbonate ions.
Carbonic anhydrase (EC 4.2.1.1) is a globular zinc metalloenzyme of molecular mass 30,000. The enzyme was discovered in 1933 and has been the subject of intense scientific investigation. Multiple isoforms have been discovered in plant and animal. The enzyme also exists in plant tissues where it is believed to facilitate the transport of carbon dioxide. Red blood cells contain isoenzymes I and II, which are the most active. Carbonic anhydrase II has the highest molecular turnover number of any known enzyme. One molecule of carbonic anhydrase can hydrate 36,000,000 molecules of carbon dioxide in a period 60 seconds. Physiologically, carbonic anhydrase facilitates the removal of carbon dioxide from the mammalian body. The general enzyme reaction is shown below in equation 1.
Equation 1:
CO2+H2O less than xe2x95x90 greater than H++CO3xe2x88x92
It is stow generally accepted that the reaction occurs as two half reactions shown below in equations 2 and 3.
Equation 2:
Exe2x80x94Znxe2x80x94H2O less than xe2x95x90 greater than Exe2x80x94Zn+Oxe2x88x92+H+
Equation 3:
Exe2x80x94Znxe2x80x94OH+CO2 less than xe2x95x90 greater than Exe2x80x94Znxe2x80x94CO3xe2x88x92+H+ less than xe2x95x90(+H2O,xe2x80x94H2O)xe2x95x90 greater than Exe2x80x94Znxe2x80x94H2O+CO3xe2x88x92
Carbonic anhydrase has been used in many studies directed at improving or testing of various methods of protein immobilization. The high molecular turnover rate of the enzyme renders it an ideal protein for these types of experiments
The presence of carbonic anhydrase in solution facilitates the transfer of carbon dioxide from the gas to the liquid phase. This effect is based on the well established laws governing the mass transfer of gases.
The management of carbon dioxide has begun to attract the attention of the scientific community, due primarily to the problem of global warming. Previous interest in carbon dioxide has been centered around the use of the gas in a variety of the processes. None of the currently employed carbon dioxide management systems involve enzymatic conversion of the gas and are therefore not relevant to the present application. Prior art processes for the management of carbon dioxide are described in the following U.S. Pat. Nos. 3,659,400; 3,853,712; 4,032,616; 4,047,894; 4,162,298; 4,452,676; 4,521,387; 4,710,362;. 5,061,455; 5,112,740; 5,609,838; 5,618,506; 5,624,812; 5,565,319; 5,674,463; and 5,690,099.
Also known in prior art, there is the process disclosed in WO 96/40414 in the name of Trachtenberg. Trachtenberg discloses a process for gas separation wherein a selected gas in a mixed gas strew is contacted by an enzyme having an active site directly contacted by the mixed gas stream, and the selected gas is at least partially removed from the mixed gas stream.
EP511719 discloses a process where carbon dioxide is being removed from a gas stream using a enzyme reactor in which carbonic anhydrase is immobilized on a porous substrate.
Moreover, the United States Air Force carried out two investigations in 1965 and 1966 an the possible use of carbonic anhydrase to remove carbon dioxide from space vehicles. The first study explored the absorption of carbon dioxide from an air stream using a closed air loop apparatus. A variety of chemicals alone and/or in combination with CA were evaluated, with respect to their capacity to remove carbon dioxide. The principle conclusion drawn was that the closed air loop system provided an adequate method to study the removal of carbon dioxide from a stream of air. The second study was directed at determining the efficiency of carbon dioxide removal from an air stream using carbonic anhydrase in the presence of various amines. The conclusion reached was that the amine solutions could possibly be used for carbon dioxide absorption and desorption in atmosphere control concepts.
Although many studies relating to the management of carbon dioxide have been conducted in prior art, there is still presently a need for a process and an apparatus that will efficaciously manage carbon dioxide rapidly and at a relatively low cost either for producing carbon dioxide a removing it from a CO2-containing gas.
An object of the present invention is to propose a process and an apparatus that will satisfy these needs.
In accordance with the present invention, that object is achieved with a process for removing CO2 from a CO2-containing gas, the process being performed in a packed tower bioreactor comprising:
a bottom chamber having a gas inlet and a liquid outlet;
an upper chamber having a liquid inlet and a gas outlet;
a reaction chamber disposed between and being in fluid communication with the bottom chamber and the upper chamber, the reaction chamber being packed with a plurality of solid supports with a non-porous surface on which surface carbonic anhydrase or analogue thereof is immobilised; the process comprising the steps of:
a) supplying the liquid inlet of the upper chamber with an aqueous liquid stream while supplying the gas inlet of the bottom chamber with a CO2-containing gas stream, the gas stream then flowing upwards into the reaction chamber
b) directing the aqueous liquid stream downwards into the packed reaction chamber to contact the CO2-containing gas with the aqueous liquid and promote diffusion of the CO2 in the aqueous liquid, and thereby allowing the carbonic anhydrase immobilized in the reaction chamber to catalyze the hydration of the diffused CO2 into hydrogen ions and bicarbonate ions;
c) evacuating from the liquid outlet of the bottom chamber a liquid solution containing the hydrogen ions and bicarbonate ions produced in the reaction chamber and evacuating from the gas outlet of the upper chamber a treated gas.
The present invention is also directed to a process far removing CO2 from a CO2-containing gas, characterized in that it comprises the step of:
a) contacting the CO2-containing gas with an aqueous liquid, preferably water, in a bioreactor containing immobilized carbonic anhydrase, or an analog thereof, the carbonic anhydrase catalysing the hydration of the CO2 into hydrogen ions and bicarbonate ions.
Preferably, prior to step a), there is a step d immobilizing carbonic anhydrase in the bioreactor. The step of immobilizing carbonic anhydrase in the bioreactor may comprise the step of covalently binding carbonic anhydrase to an inert solid support material mounted in the bioreactor. The step a) of contacting the CO2-containing gas with an aqueous liquid comprises the steps of directing a stream of the CO2-containing gas upwards into the bioreactor and directing a stream of the aqueous liquid downwards such that the stream of CO2-containing gas flows countercurrent the stream of the aqueous solution.
According to a first preferred embodiment of the present invention, the process comprises, after step a), step b) of feeding the hydrogen ions and bicarbonate ions obtained in step a) into a second bioreactor containing immobilized carbonic anhydrase which catalyses the conversion of the hydrogen ions and the bicarbonate ions into concentrated CO2 and water.
According to a second preferred embodiment of the invention, the process comprises, after step a), the step of feeding the hydrogen ions and bicarbonate ions obtained in step a) into an ion exchanger containing hydroxyl ions so that the bicarbonate ions are exchanged for the hydroxyl ions which are then free to combine with hydrogen ions to form water.
The present invention also relates to an apparatus for the management of CO2 using immobilized carbonic anhydrase or analog thereof. The apparatus comprises an upright bioreactor.
The bioreactor comprises a bottom chamber having a gas inlet to receive a CO2-containing gas and a liquid outlet to evacuate from the bioreactor a liquid solution containing hydrogen ions and bicarbonate ions produced in the bioreactor. The bioreactor further comprises an upper chamber having a liquid inlet to receive an aqueous liquid and a gas outlet to evacuate any gas from the bioreactor.
A reaction chamber is disposed between and is in fluid communication with the bottom chamber and the upper chamber. This reaction chamber is characterized in that it comprises a plurality of solid supports mounted therein for covalently immobilizing carbonic anhydrase.
In use, the CO2-containing gas is fed through the gas inlet and an aqueous liquid, preferably water, is fed through the liquid inlet. The CO2-containing gas and the aqueous liquid flows through the reaction chamber where carbonic anhydrase therein catalyses the hydration at CO2 thereby forming hydrogen ions and bicarbonate ions. Then, the solution containing the hydrogen ions and bicarbonate ions flows out from the bioreactor via the liquid outlet and the gas free from CO2 flows out via the gas outlet.
According to a first preferred embodiment of the present invention, the apparatus comprises a second bioreactor in series with the upright bioreactor which is hereinafter called a first bioreactor. The second bioreactor is substantially similar to the first bioreactor. It comprises a liquid inlet connected with the liquid outlet of the first bioreactor to receiving the liquid solution from the first bioreactor.
A reaction chamber is provided in order to contain carbonic anhydrase. This reaction chamber is in fluid communication with the liquid inlet and comprises a plurality of inert organic supports mounted therein for covalently immobilizing carbonic anhydrase. The reaction chamber is in fluid communication with a gas outlet to evacuate a gas containing carbon dioxide obtained in the chamber.
A liquid outlet is in fluid communication with the reaction chamber to evacuate water obtained in the reaction chamber
The second the preferably comprises means for controlling a pressure in the reaction chamber of the second bioreactor.
According to a second preferred embodiment of the present invention, the apparatus further comprises an ion exchanger having an inlet for receiving the liquid solution from the bioreactor.
The present invention is also directed to the use of carbonic anhydrase or analog thereof covalently immobilized in a bioreactor to remove carbon dioxide from a CO2-containing gas, a to produce hydrogen and bicarbonate ions, a to the use of carbonic anhydrase or analog thereof covalently immobilized in a bioreactor to produce CO2 from enriched solutions of hydrogen: and bicarbonate ions.
A non restrictive description of preferred embodiments will now be given with reference to the appended drawings.